Measuring Brain Activity
Methods for Studying the Brain
- Single Cell Recording
- Electrode through skull and into brain.
- Records differences in electrical potential over time in a
single neuron or small group of neurons.
- Action potentials
- All-or-none firing
- Firing rate varies depending on strength of input.
- Excellent temporal and spatial resolution
- Electroencephalogram (EEG)
- Electrodes placed on scalp.
- Each electrode measures changes in electrical potential at
its location.
- Measurement from each electrode reflects activity from
large numbers of neurons.
- Neurons near brain surface produce stronger signals than
those deep in the brain.
- Signals can be combined to produce maps of activation
across brain surface.
- Temporal resolution excellent. Spatial resolution not as
good.
- X-Ray Computed Tomography (CT or CAT)
- Multiple X-ray images
- Combined computationally
- Produces images of slices through brain (or other parts of
body).
- Very useful for localizing damage.
- Shows only structure, not function.
- Positron Emission Tomography (PET)
- Radioactive substance introduced to bloodstream
- Ring of detectors around head record positrons from
radioactive decay
- Active areas of brain receive more blood, and thus produce
more positrons.
- Can computationally produce images of brain slices.
- Different colors show different levels of blood flow and
thus different levels of brain activity.
- Shows function, but not structure.
- OK spatial resolution. Poor temporal resolution.
- Nuclear Magnetic Resonance Imaging (MRI)
- Giant magnet creates strong magnetic field.
- Molecules align to magnetic field.
- Sudden radio pulse knocks them out of alignment.
- Different types of molecules produce different
responses.
- Can produce maps showing concentrations of different
substances
- Shows structure, not function.
- Functional Magnetic Resonance Imaging (fMRI)
- Use MRI to measure blood flow (and therefore activity) in
brain.
- Shows brain function.
- Colors representing different levels of activity can be
added to structural images of brain slices or brain
surface.
- Both spatial and temporal resolution improving.
- Transcranial Magnetic Stimulation (TMS)
- Produces brief magnetic pulse.
- Can interfere with brain activity within small region near
surface.
- TMS in motor areas can produce sudden movement.

Psych 391D:
Consciousness
Kyle Cave
Psychology Dept.
U.
Mass.